The disclosure of Japanese Patent Application No. HEI 10-33613 filed on Feb. 12, 1999 including the specification, drawings, and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a control apparatus for a vehicle provided with a power source and a continuously variable transmission which is capable of continuously varying the gear ratio, and more particularly to a control apparatus and a control method, each of which is capable of canceling backlash which is present in a drive system and which causes vibrations in the longitudinal direction of the vehicle (backing or transient surge and shock) to be produced.
2. Description of the Related Art
It is known that when the gear ratio of a continuously variable transmission of a vehicle provided with the continuously variable transmission is raised to meet a requirement for accelerating the vehicle or a requirement for increasing output by demand made through depression of an accelerator pedal or the like, vibrations are produced in the longitudinal direction of the vehicle at a moment of completion of the gear change. The foregoing occurrence is called xe2x80x9cbacking or transient surgexe2x80x9d which is caused by inertia torque or the elasticity of a power transmission system. That is, when the gear ratio of the continuously variable transmission is raised to meet the requirement for increasing the output from the power source such as an engine, or the requirement for accelerating the vehicle, the number of revolutions of a rotor of the transmission of power is changed. Therefore, inertia torque corresponding to the variation of the number of the revolutions (the angular acceleration) and the inertia moment is generated. When the number of revolutions of the rotor is stabilized to a required number of revolutions after the gear shift has been completed, the inertia torque is relieved. As a result, the inertia torque temporarily increases the drive torque, causing longitudinal vibrations to be generated owing to the deflection elasticity of the power transmission system.
An apparatus for preventing longitudinal vibrations of the vehicle of the foregoing type has been disclosed in Japanese Patent Laid-Open No. HEI 8-177997. The disclosed apparatus is designed to control the gear ratio to prevent vibrations in the longitudinal direction of the vehicle. That is, the moment at which the gear shift completes is obtained in accordance with a target gear ratio and a present gear ratio. Moreover, the half period of the vibrations of the vehicle in the longitudinal direction which are expected to be generated upon completion of gear shift is predicted in accordance with input torque corresponding to the gear ratio and an actual gear ratio. Thus, the gear ratio is forcibly corrected to a gear ratio by which the vehicle speed is raised at the time of a half period of the vibrations of the vehicle in the longitudinal direction before the moment at which the gear shift is completed. When the foregoing control is performed, about half of the inertia torque is relieved at the time of the half period before the moment at which the gear shift is completed. Therefore, the peak of the vibrations substantially coincides with the moment at which the gear shift is completed. When the torque caused from the vibrations is afterwards reduced, the residual inertia torque is relieved. As a result, the inertia torque acts to prevent vibrations. This control will be hereinafter referred to as a backing or transient surge preventive control.
The backing or transient surge preventive control realized by the apparatus disclosed in Japanese Patent Laid-Open No. HEI 8-177997 is structured such that the gear ratio is controlled only when the gear shift is completed. Therefore, there is apprehension that vibrations of the vehicle in the longitudinal direction occurring when the acceleration is started cannot completely be controlled. An apparatus proposed by the applicant of the present invention in Japanese Patent Application No. HEI 10-119772 is capable of effectively preventing vibrations of the vehicle in the longitudinal direction when both the output of the power source and the gear ratio of the continuously variable transmission are changed. According to the foregoing disclosure, the apparatus is provided with means which is structured such that when the output torque of the power source is controlled to correspond to the inertia torque generated owing to change in the gear ratio, the output torque of the power source is controlled to torque corresponding to the inertia torque and the target torque determined in accordance with the requirement for changing the drive force. The foregoing apparatus is able to effectively control the vibrations of the vehicle in the longitudinal direction caused from change in the drive force even when the gear shift is started following the request for a change of power source output.
Each of the foregoing apparatuses provides theoretical control realized with an ideal model having a drive system provided with a power source and a continuously variable transmission and is free from backlash and the like. Note that an actual vehicle includes a multiplicity of non-linear elements (for example, looseness caused by the backlash of the gear portions of the drive system and the spline portions). When the drive state is changed from a driven state in which the power source such as the engine is driven by the wheels connected to the continuously variable transmission to a driving state in which the output of the power source is transmitted to the wheels to drive the wheels, the backlash of the drive system exerts a great influence. That is, the kinetic energy accumulated during the motion as backlash is impulsively transmitted when the state of driving is changed. Moreover, output transmission timing of the power source is deviated. As a result, there arises a problem in that a structure constituted by adapting the foregoing control to an actual vehicle encounters generation of impact at an unintended time, and a deviation of the timing of the prevention control. Hence it follows that the vibrations of the vehicle in the longitudinal direction cannot satisfactorily be prevented. Thus, there arises a problem in that a person riding in the vehicle feels discomfort.
In view of the foregoing, an object of the present invention is to provide a control apparatus for a vehicle provided with a power source and a continuously variable transmission which is capable of quickly and adequately canceling backlash when the relationship between a power source and wheels connected to the continuously variable transmission is alternately changed between a driven state and a driving state in a case of a vehicle having the backlash in the drive system, and sufficiently reducing vibrations of the vehicle in the longitudinal direction owing to cancellation of the backlash so as to prevent any uncomfortable feeling for a person in the vehicle.
To achieve the foregoing object, according to a first aspect of the present invention, there is provided a control apparatus for a vehicle provided with a power source and a continuously variable transmission, comprising a backlash preventive control unit structured such that when a driving state and a driven state between the power source and the continuously variable transmission and wheels connected to the power source and continuously variable transmission through a drive system are alternately changed, the backlash preventive control unit cancels backlash present in the drive system so as to prevent vibrations of the vehicle caused from the backlash.
The backlash of the drive system is backlash which is present in a gear portion and a spline portion which transmit driving force. Note that the amount of each backlash was previously determined when the drive system was designed. The expression xe2x80x9ccancellation of backlashxe2x80x9d means to reduce the gaps of the tooth flanks of the gear portions and spline portions caused from the backlash in a direction in which the drive force is transmitted. Thus, the contact is realized when the power source and the continuously variable transmission is changed from the driven state to the driving state with respect to the wheels. Thus, impulsive collision of the tooth flanks is prevented.
The foregoing structure is arranged such that the backlash is canceled in advance when the driven state and the driving state are switched. Therefore, impact which occurs when the switching takes place can be prevented. As a result, vibrations of the vehicle in the longitudinal direction can sufficiently be reduced. As a result, discomfort for a person in the vehicle can be prevented. When control of backing or transient surge is implemented after the backlash has been canceled, more effective control of the backing or transient surge can be performed.
The backlash preventive control unit may be structured such that output of the power source during the preventive control or the output of the power source and period in which the output is controlled are determined in accordance with factors which exert an influence on the friction of the power source so as to cancel the backlash.
The factors which exert an influence on the friction of the power source include the number of revolutions of the power source, the water temperature, the oil temperature and whether or not an auxiliary device (for example, an air conditioner, an alternator, head lights, a power steering unit or a generator of a hybrid car) is being operated.
With the foregoing structure, torque for maintaining the number of revolutions of the power source required to adequately cancel the backlash in a state of actual drive of the vehicle or a control time required to adequately cancel the backlash can be obtained. As a result, smooth control for preventing backlash can be performed. Since the backlash is prevented, vibration of the vehicle in the longitudinal direction can sufficiently be reduced. Thus, discomfort for a person in the vehicle is prevented.
The backlash preventive control unit may be structured such that output of the power source during the preventive control or the output of the power source and period in which the output is controlled are determined in accordance with the gear ratio of the continuously variable transmission and the vehicle speed so as to cancel the backlash.
The shock and backing or transient surge caused from the backlash can easily be sensed by a person in the vehicle as the gear ratio is high or as the vehicle speed is low. Therefore, control for preventing backlash is performed slowly such that the output of the power source is reduced and a control period is made longer in a case where the gear ratio is high or in a case where the vehicle speed is low. As a result, the degree at which the backing or transient surge and the shock is sensed by a person in the vehicle can be lowered. When the gear ratio is low or the vehicle speed is high, the output of the power source for preventing the backlash is increased and the control period is shortened. As a result, the control for preventing the backlash can be quickly performed. Thus, shift to subsequent control of acceleration or the control for preventing backing or transient surge can be quickly performed. As a result, discomfort for a person in the vehicle can be prevented while control in which priority is given to the response is being performed.
The backlash preventive control unit may perform a short-period control in which prevention of the backlash is completed in a short time when the power source and the continuously variable transmission are changed from a driven state to a driving state and a long-period control in which prevention of the backlash is completed in time longer than the short-period control which is implemented when the driving state is changed to the driven state.
As a result of the foregoing structure, when the power source and the continuously variable transmission are changed from the driven state to the driving state, that is, when acceleration of the vehicle is required, the control for preventing the backlash is performed in a short time. In this case, the degree of vibrations in the longitudinal direction sensed by a driver can be lowered. Moreover, control can be performed in which any delay in the next operation is not sensed and priority is given to responsiveness. When the power source and the continuously variable transmission are changed from the driving state to the driven state, that is, deceleration of the vehicle speed is required, the control for preventing the backlash is performed for a long time. In this case, the control for canceling the backlash is performed slowly. Thus, the degree of vibrations of the vehicle in the longitudinal direction sensed by the driver can furthermore be lowered. As a result, control can be performed in which priority is given to the riding comfort of the vehicle.
The backlash preventive control unit may be structured to determine the switch between the driven state and the driving state in response to a signal supplied from an idle switch so as to cancel the backlash.
The foregoing structure enables the backlash preventive control unit to detect a direction in which the power source and the continuously variable transmission are switched between the driving state and the driven state in accordance with whether the idle switch is switched on or switched off. Therefore, control of preventing backlash adaptable to a state of driving of the vehicle can be performed with a simple structure.
The backlash preventive control unit may be structured to determine the switch between the driven state and the driving state in accordance with the relationship between predicted friction torque of the power source and torque of the power source shown in a graph so as to cancel the backlash.
The predicted friction torque is torque calculated in accordance with the number of revolutions of the power source, the water temperature, the oil temperature and whether or not the auxiliary device is being operated. The torque shown in the graph is torque obtained from an indicator graph of a combustion chamber of the power source and realized through actual combustion.
According to the foregoing structure, when the predicted friction torque is larger than the indicator torque, the power source and the continuously variable transmission are in the driven state. When the predicted friction torque is smaller than the indicator torque, the power source and the continuously variable transmission are in the driving state. The backlash preventive control unit compares the two types of torque with each other to accurately and quickly recognize switch between the driving state and the driven state so as to perform adequate control for preventing the backlash.
The backlash preventive control unit may be structured to recognize completion of the period in which the prevention is controlled in accordance with change in the vehicle speed so as to complete cancellation of the backlash.
Since the quantity of the backlash is known when the drive system was designed, the control period and completion of the control period can be selected from a plurality of adequate values predetermined in accordance with the output of the power source and the vehicle speed. According to the above-mentioned structure, the change in the vehicle speed or the like occurs at the instant when the backlash has been canceled in the direction in which the power of the drive system is transmitted. Thus, completion of the preventive control can easily be predicted. As a result, the overall structure of the control can be simplified.
The backlash preventive control unit may be structured such that when the power source and the continuously variable transmission are changed from the driven state to the driving state, the gear ratio of the continuously variable transmission is changed to the speed increase side before the output of the power source is increased to cancel the backlash of the drive system. Then, the output of the power source may be increased and the gear ratio of the continuously variable transmission is changed to the speed decrease side.
According to this structure, effective backlash control for directly canceling the backlash may be performed by temporarily changing the gear ratio of the continuously variable transmission to the speed increase side and temporarily decreasing the speed of the CVT.
The backlash preventive control unit may be structured such that when the power source and the continuously variable transmission are changed from the driven state to the driving state, at least one of the output of the power source and the gear ratio is controlled to make a rise in the number of revolutions of the power source to relatively be higher than a rise of the number of revolutions of the wheels so as to cancel the backlash.
Since the foregoing structure is arranged such that the rotations of the wheels are gradually brought closer to those of the power source, the backlash can be directly and smoothly canceled. As a result, control of the backlash can be performed more effective.
According to a second aspect of the present invention, there is provided a method of controlling a vehicle provided with a power source and a continuously variable transmission which is capable of continuously varying the gear ratio, the method comprising the steps of detecting a switch between a driving state and a driven state between a power source and a continuously variable transmission on one hand and wheels connected through a drive system on the other hand; and canceling backlash present in the drive system when the driving state and the driven state are alternately changed between the power source and the continuously variable transmission on one hand and the wheels on the other hand so as to prevent vibrations of the vehicle caused from the backlash.
According to the foregoing control method, the backlash can be canceled in advance when the switched is performed between the driven state and the driving state. Therefore, impact which is produced when the switch occurs can be eliminated. As a result, vibrations of the vehicle in the longitudinal direction can sufficiently be reduced. Hence it follows that discomfort for a person in the vehicle can be prevented.